The invention relates to the area of ear protection devices, specifically an earplug provided with a piezoelectric element that converts electrical signals into oscillations. The invention also relates to various methods for manufacturing these earplugs.
Earplugs, which serve both for auditory protection and for listening, have numerous applications. As one widely used principle, an earplug has an electroacoustic converter on one of its front parts. In order for the sound waves to reach the eardrum, the earplug has an interior canal that transmits the sound from the acoustic converter to the eardrum through the air. This principle, with a small loudspeaker and a canal open on one side, enables sound to be conducted through the air, as already presented in DE 39 16 995 C2 for example. These earplugs with a built-in listening device often have excellent acoustic properties, but their design is very complicated so that they are very expensive to manufacture. For better understanding, it will be noted that the aforementioned earplugs also have a device enabling them to be used also as microphones.
DE 28 49 152 B1 presents an earplug in the same family provided with a piezoelectric element that converts the electrical signals into oscillations. In other words, the piezoelectric element is designed to operate in a listening mode. The piezoelectric element also acts as a microphone. The earplug has a rigid housing in the shape of a hard metal or plastic plug designed to be inserted into the external auditory canal. The piezoelectric element with a weight is mounted in the cavity of the housing like a built-in beam. The aim is to reduce feedback effects when the piezoelectric element is used as a microphone.
There also exists earplugs with a piezoelectric element described solely for microphone use. In this regard, mention will be made of patents in which the piezoelectric element is built into a rigid body such as in DE 2810716 for example, or a semi-soft body made of RTV silicone rubber but stiffened by a spring as in U.S. Pat. No. 4,696,045 for example, the spring also serving to protect the piezoelectric element. In operation, the user's voice is conducted from his throat to the bones of the head, then through the wall of the auditory canal. Hence, it is transmitted by bone conduction. The use of a rigid body or semi-soft body stiffened by a spring is unpleasant, even irritating or painful, for the user.